1. Field of the Invention
The present invention relates to magnetostatic wave devices and, more particularly, to a magnetostatic wave device comprising a magnetic garnet film, the material of said magnetic garnet film being represented by a general formula: EQU (Y.sub.1-r R.sub.r).sub.3 (Fe.sub.1-a A.sub.a).sub.5 O.sub.12
where R is at least one material selected from among La, Bi, Gd and Lu; A is at least one material selected from among Al, Ga, In and Sc; r and a are within the ranges 0.ltoreq.r.ltoreq.1 and 0.ltoreq.a&lt;1, respectively; and r and a are not be zero at the same time.
2. Description of the Related Art
The trend toward intense exchange of information has resulted in increasing needs for microwave devices for processing signals in microwave bands recently. Referring especially to devices for analog processing, development is active on signal processing devices such as resonators, filters and S/N enhancers. As materials used for such magnetostatic wave devices, magnetic garnet materials represented by YIGs are primarily used.
A YIG is formed as a film on a single crystal substrate made of gadolinium gallium garnet (GGG), samarium gallium garnet (SGG), neodymium gallium garnet (NGG) or the like primarily using a liquid phase epitaxial process (LPE process) and in a configuration integral with the substrate.
FIG. 1 shows a noise filter, which is one example of magnetostatic wave device. The noise filter includes a GGG substrate 1 and a garnet single crystalline film 2 provided on the GGG substrate 1. The noise filter further includes a pair of electrodes 3 provided on the garnet single crystalline film 2. In FIG. 1, the reference symbol H denotes the direction of the applied external magnetic field, Iin denotes the direction of entering the microwave, W denotes the direction of propagation of magnetostatic surface wave (MSSW), and Iout denotes the direction of the generation of the microwave.
For the purposes of adjusting the magnetic characteristics of such a YIG and matching the lattice constant thereof with that of the substrate, it is actively attempted to design materials with various elements substituted for the C-site (the position of Y) and the A, D-site (the position of Fe) of a YIG. The terms "C-site" and "A, D-site" are representations used to represent a magnetic garnet material using a general formula: C.sub.3 (A, D).sub.5 O.sub.12. Such substitution R, A:YIGs (substitution yttrium-iron-garnets) are becoming dominant materials for magnetostatic wave devices.
A single crystal is considered preferable when it has no variation in composition as a whole and is uniform from a crystallographical point of view. Highest possible uniformity has been pursued also in the development of substitution R, A:YIGs manufactured using LPE processes.
However, a problem has existed in that the half-value width (.DELTA.H) of ferromagnetic resonance, which is an important magnetic property for a substitution R, A:YIG used for a magnetostatic wave device, can not be preferable when the thickness of the film is small, and specifically, when the film thickness is 6 .mu.m or less. In addition, conventional magnetostatic wave devices have not been successful yet in satisfying the demand for devices having an operational frequency band as wide as possible, which is a characteristic required for various reasons including compensation for temperature characteristics.
It is therefore a primary object of the present invention to provide a magnetostatic wave device which operates even with a substitution R, A:YIG having a small film thickness and which has a wider operational frequency band.